Electro-optical image producing system



April 2, 1940. KNQOP 2,195,864

ELECTRO-OPTICAL IMAGE PRODUCING SYSTEM Filed NOV. 20, 1935 2Sheets-Sheet 1 April 2,. 1940. w KNQQP ELECTED-OPTICAL IMAGE PRODUCINGSYSTEM Filed Nov. 20. 19:55

2 Sheets-Sheet 2 INVENTOR M. A. K/VO 0P Patented Apr. 2, i

ergo-omen. macs raonuomo SYSTM whom a. Knoop, West Hempstead, 51s.,assignor to Bell Telephone Laboratories, Incorporated, New York, York N.Y a corporation or New Application November-2o, 1935, Serial No. saess22 Claims.

10 a current of sine wave form into current impulses of rectangular waveform, the duration of each impulse being small compared to the period ofthe sine wave.

In accordance with a specific embodiment of the invention herein shownand described for the purpose of illustration, there is provided at atransmitting station apparatus for repeatedly scanning the elementalareas in succession of 2. held of view along successive parallel linesto 20 produce a television image current, each complete scanning of thefield of view taldng place within the period of persistence of vision.At the receiving station there is provided a bank or lightmltting'elements arranged in rows corresponding to the parallel scanningpaths at the transmitter, there being one lamp corresponding to eachelemental area of the field of' view. For example. there may be onehundred lamps in each horizontal row and one hundred 3O lamps in eachvertical column, making ten thousand lamps in all. One set of terminalsof the lamps of each row is connected together to a contact of amechanical distributor, while the other lamp terminals of each columnare connected together to the anode of a three-electrode thermionictube, thus making a coordinate system. A mechanical commutator selectsthe rows of lamps in synchronism with the scanning of successlvelincs ofthe field of view at the transmitting station. The source of imagecurrent is impressed upon the horizontal rows of lamps in successionthrough the mechanical distributor.

The vertical column of lamps must be selected in sequence at a rapidrate and-this is done by a non-mechanical commutating arrangement; Ii alamp bank of ten thousand lamps is tdbe commutated in one-twentieth of asecond, for example, there is employed atransmission path dred sections,each having inductive and eaor relay network having characteristics suchthat pacitive elements. The control electrodes of th thermionic devicesare connected to different network sections; respectively. Theelectrodes are normallynegatively biased to such a degree that the lampsemit no light or only a control very small amount of light. A highamplitudeimpulse of a duration preferably equal to the time required forseaming a single elemental area, .000005 second in the above example, isperiodically impressed upon the delay network at a rate equal to theline -scanning frequency andthis impulse increases the grid potential ofthe thermionic tubes in succession to zero, for example, thus causingthe lamps in succession to emit light of an intensity determined by theamplitude of the image current.

The periodic starting impulses impressed upon the delay circuit arederived from a source oi alternating current, the frequency of which isequal to the line scanning frequency. Each alternating current cyclelsconverted into a squaretopped unidirectional current having a durationapprommately equal to one-half cycle of the alternating current and eachsquare-topped current impulse is converted into .an impulse ofelectromotive force of logarithmic wave form having a high amplitude andthe top of this wave is cut oil, thus forming an approximatelyrectangular wave having a duration less than the time required forscanning a single elemental area.

Any suitable arrangement may be employed for maintaining synchronismbetween the scannings at the transmitting and receiving stations and formaintaining the correct relationship between the rate at which thelogarithmic impulses are generated and the speed of themechanicalcommutator at the receiving station. For example, a constant frequencyvacuum tube oscillator may be employed for generating the alternatingcurrent from which the logarithmic impuises are derived and current fromthis oscillator may also be supplied to a circuit for controlling the'speed of a. motor which drives the mechanical commutator at the receiverand to a circuit for controlling the speed of a motor which drives ascanning disc or other apparatus for scanning the field of view at thetransmitting station.

InFlgs. 1 andlA of the drawings there is disclosed, for the .purpose ofillustration, 9. complete television system embodying the features ofthe invention.

Fig. 2 shows a modification of the system shown in Fig. 1.

Referring to Figs. 1 and 1A or the drawings,

' areas of the field of view are thus illuminated in at the televisiontransmitting station A the scanning disc I8 is driven by the motor 85 ata speed of 16 or more revolutions per second to cause light from sourceI I directed through th spirally arranged apertures I2 of the scannindisc to illuminate the elemental areas in succession of a field of viewdefined by the opening in screen l3 and including the subject l4.Elemental succession along successive parallel lines. Light reflectedfrom the subject l4 impinges upon one or more light sensitive cells i 5and the varying current produced by the action of the light sens sitivecells, after being amplified by the vacuum tube amplifier I6, istransmitted to the distant station B through a transformer I! and atransmission channel l8.

A source of alternating current of constant frequency produced by anoscillator 88 may be connected to a winding of transformer 42 by meansof a switch 48. Current from this constant requency source, after beingamplified by the vacuum tube amplifier 43 is impressed upon the speedcontrol apparatus 31 for maintaining the motor 35 at a constant speedunder control of the constant frequency current from source 38. Thisspeed controlling arrangement is disclosed more in detail in Patent No.1,999,376, granted to H. M. Stoller, April 30, 1935. Current from theconstant frequency source 38 is also transmitted to the image producingstation B over the line 41 to maintain the image production at station Bin synchronism with the scanning of the field of view at station A.

At the receiving station B television images of the field of viewscanned at station A are produced upon the image producing lamp bankcomprising a plurality of lamps or lamp elements 50, one for eachelemental area of the field of view.

. These lamps may be glow discharge lamps, for

example. Each transverse row of lamps corresponds to a scanning line ofthe field of view and if the field of view is square, the number of rowsof lamps are equal to the number of vertical 'columns, as shown. Whileonly six rows and columns of lamps are shown, any desired number may beemployed. If, for example, the field of view at the transmitter isscanned along 100 parallel scanning lines, a lamp bank having 100"mechanical distributor 54.

rows of 100 lamps each may be employed.

The television image current received from station A over line i8 istransmitted through transformer i9 and amplified by vacuum tubeamplifiers 20 and 5!. The output circuit of vacuum tube amplifier 5!comprises a battery 52 the negative terminal of which is grounded and aresistive element 58. The anode of amplifier 5! is connected to theanodes of the rows of glow discharge'lamps 50 in succession by means ofthe This distributor has a number of contacts equal to the number ofrows of lamps 50 and is driven by a motor 55 in synchronism with thescanning disc 10 at the transmitting station. Current from the constantfrequency current source 38 received over line 41. after beingtransmitted through transformer 44. amplified by amplifier 45. andtransmitted through the phase shiftin transformer 56 is impressed uponthe speed control apparatus 51 like apparatus 81 for controlling thespeed of motor 58.

The constant frequency current received over line 41 after beingamplified by the amplifier 45 and transmitted through the phase shifter56 is also impressed upon the primary winding of transformer 58 forcontrolling the circuit comprising the similar vacuum tubes 58 and 88 toproduce a square-topped unidirectional voltage having a fundamentalfrequency equal to the frequency'of the constant frequency currentsource 38. The grids of each of the tubes 59 and 88 are negativelybiased by the battery 8|. The grid of tube 58 is also biased due to thepotential drop across resistive elements 88, 81, 88 in response to anodecurrent from source 89 and the grid of tube is biased due to thepotential drop across resistive elements 62, 83, 84 in response to theflow of anode current from source 85. The cathode-anode circuit of tube88 comprises resistive elements 62, 83 and 84 and battery 85, while thecathode-anode circuit of tube 88 comprises resistive elements 86, 81 and88, like resistive elements 82, 88 and 84, respectively and battery 69,like battery 85. An adjustable contact on resistive element 84 isconnected to the control electrode of vacuum tube 88 while an adjustablecontact of resistive element 88 is connected to the control electrode ofvacuum tube 58. One terminal of the secondary winding of transformer 58is connected to a common treminal of resistive elements 62 and 88 andthe other terminal is connected to a common terminal of resistiveelements 88 and 81. The circuit elements are so chosen, that whencurrent fiows in the anode circuit of vacuum tube 88, the grid of vacuumtube 88 is negatively biased to such a potential that no current canfiow in the anode circuit of vacuum tube 60 and that when current fiowsin the anode circuit of vacuum tube 6|! the grid of vacuum tube 59 isnegatively biased to such a potential that no current can flow in theanode circuit of vacuum tube 58. There is thus generated between thenegative terminal of battery and ground a unidirectional electromotiveforce of square-topped wave form, one such square-topped impulse beingproduced for each cycle of the current impressed upon the transformer58.

During the periods that current is flowing in the anode circuit ofvacuum tube 59, a portion of the anode current from battery 65 flowsthrough the potentiometer winding 10 and resistive element H to chargethe condenser 72. When anode current is not flowing through tube 59, thecondenser is discharged through a circuit including resistive elements62, 68, 64, i0 and H, one terminal of resistive element 82 and oneterminal of resistive element 70 being grounded. The circuit elementsmay obviously be so chosen that the condenser is charged at a rapid rateto a high potential less than the potential drop across resistiveelements 62, 63 and 64 during one-half cycle of the current from source88 and is rapidly discharged during the next half cycle of the currentfrom source 38. The charging-discharging current of logarithmic waveformfiowing through the resistive elements 10 and II produces anelectromotive force of corresponding wave form which is applied to theinput circuit of three electrode vacuum tube I3. The grid of this vacuumtube is negatively biased by the battery 14 to such an extent thatcurrent flows in the anode circuit of vacuum tube 18 only when dischargecurrent of considerable amplitude is flowing from condenser 12 throughresistive elements 10 and H. Moreover, the anode current of vacuum tube18 reaches saturation when the amplitude of the condenser dischargecurrent is less than its maximum value. Therefore, during each cycle ofthe alternating current from source 18 vacuum tube it a current impulseof extremely short duration and of considerable amplitude. The, waveshape of this impulse is'substantially rectangular. The output circuitof vacuum tube 73 is connected to theinput circuit of vacuum tube itthrough a coupling condenser 80 and resistive element ?5.

In the output circuit of vacuum tube 55 there is connected a. battery 11and a delay network 82 of a plurality of sections. The delay network isso designed that the diflerent sections, respec tively, introducesubstantially the some delay and so that the phase distortion introducedby one section is compensated for by the phase distortion introduced byan adjacent section, thus making any pair of sections substantially freeof phase distortion. If desired, each section may be so designed as tointroduce the same delay for all frequencies over a wide range. As shownin the drawings, the T-type sections each comprise two equal inductiveelements 5| and a capacitive element 92, while each of the bridgedT-type sections comprise the two equal inductive elements .93,capacitive element 94 and capacitive element 55. Satisfactory resultshave been obtained by employing a network of this type in which theinductive elements 9|, comprising two windings on a single core tappedin the center, has a total inductance of .0232 henries, the capacitiveelements 92 .00575 microfarads, the inductive elements 93 each .01162hen'ries, the capacitive elements as .00576 microfarads, and thecapacitive elements 95 .00144 microfarads. The .value of the terminatingresistive element 8! was 2010 ohms. The input circuits of the vacuumtubes BI are connected to the terminals of different sectionsrespectively of the delay network 82. There are as many vacuum tubes BIas there are columns of neon lamps E0, the cathodes of the lamps of' acolumn being connected to the'anode .of the vacuum tube 8| whichcontrols the lamps of that column. Due to the potential of battery ii,the grids of vacuum tube II are normally negatively biased to such anextent that the current from battery 52 flowing through the lamps 5i! ofa row connected in circuit by the commutator 54 and the anode circuitsof vacuum tubes CI is of such amplitude that the lamps emit no light oronly a small amount of light such as would be produced to representblack tone value. The negative bias is the same for all of the vacuumtubes, in the absence'of a starting impulse imsuitable value of capacitythe impulse impressed upon the delay network ,82 may be madesuiilciently brief so that the grid bias of only one of the tubes 8| atatime is-rendered less negative than the normal negative biasingpotential with the result that only one lamp 5| at a time will emitlight in accordance with-the tone value ofthe elemental area of theimage to be produced under control of the image potentials impressedupon the input circuit of vacuum tube. II.

It is thus apparent that the lamps 5|. 0! the image producing lamp bankare energized one at a time in succession in synchronism with the ofthis type is disclosed in Patent 1,999,376,

granted to H. M. Stoller April 30, 1935.

Instead of employing a large number of individual lamps, one for eachelemental. area, a plurality of multi-electrode lamps of the typedisclosed in Patent 1,759,504, granted to F. Gray May 20, 1930, one foreach line, may be employed as shown in Fig. 2. In this arrangement,instead of impressing a direct current having the image currentvariations upon the circuits of lamps through the distributor 54, asshown in Fig. 1, the received image current after being amplified by theamplifier I20 is impressed upon an oscillator-modulator I5I to producein itsoutput circult a high frequency alternating current modumay bemaintained constant.

The individual electrodes are preferably formed on the glass tubingforming the gas chamber by first covering all portions of the tube,except the portions at which the electrodes are to be formed. with asuitable material, such as adhesive tape. The exposed portions of theglass tubing are sand blasted to roughen the surface of the glass andthese portions are then covered with a suitable metal by means of aSchoop gun. The adhesive tape is then removed and contact is made witheach electrode I by tying a fine wire around the lass tube so as to makecontact with the electrode. The electrodes I55 of each column areconnected to the anode of one of the three-electrode vacuum tubes I8I.The cathodes of these vacuum tubes are connected to ground as is alsoone side of the source of modulated high frequency image current fromoscillator-modulator I5I. As in the arrangement shown in Fig. 1, thecontrol electrodes of the vacuum tubes IOI are connected to difierentsections, respectively, of a delay network I82. The anode of each vacuumtube I8I is also connected to a source of direct current I55 .through achoke coil I51 which prevents the high frequency modulated current fromflowing to ground through the battery'l56. It is thus apparent that whenthe anode-cathode impedance of one of the vacuum tubes I8I is reduced,due to a positive impulse impressed upon its" grld, a circuit iscompleted from the grounded source of high frequency modulated imagecurrent at the output of oscillator-modulator I SI,

through a contact of distributor I54, one of the common electrodes I52,I53, one of the individual electrodes I55, the anode of one of thevacuum tubes Ill, and thence to grounded cathode of the. vacuum tubeI8I. As will be understood from a consideration of the above descriptionin connection with Fig. 1, a glow discharge is thus produced atdifferent positions in succession of the multi-electrode lamp bank toproduce an image.

What is claimed is:

1. In combination, a plurality of electric discharge tubes, an input andan output circuit for each of said tubes, a plurality of signalresponsive means each connected in the output circuit of one of saidtubes, a source of electromotive force the amplitude of which varies inaccordance with signals connected in said output circuits, a delaynetwork having a plurality oi! delay sections connected in series, theinput circuits of said electric discharge tubes being connected todiilerent sections respectively of said delay network, and means forimpressing an electric impulse upon said delay network to cause saidsignal responsive means to be energized in succession in accordance withthe amplitude of said signaling electromotive force.

2. In combination, a source of alternating current, means for convertingsaid alternating current into a unidirectional current having asquare-topped wave form and a fundamental frequency corresponding tothat of said alternat ing current, means for converting said current ofsquare-topped wave form into current impulses of logarithmic wave form,and means for converting said current impulses of logarithmic wave forminto current impulses of high amplitude and of brief duration comparedwith the duration of said square-topped wave impulses.

3. In combination, a transmission network having a plurality of sectionsdirectly connected in series, each comprising inductive and capacitiveelements, means comprising an electric discharge device for generatingperiodic impulses,

means for impressing said periodic impulses uponsaid network, and aplurality of devices responsive tosaid impulses associated withdiflerent sections of said network respectively, each impulse having aduration less than the time required for transmitting it through one ofsaid sections, thus causing said devices to be operated in succession.

4. In combination, a tron network having a plurality 01' sectionsdirectly connected 1 .0 in series, each section comprising inductive andcapacitive elements, a plurality of electronic devices each having acontrol electrode connected to dlii'erent sections respectively oi. saidnetwork, a source of electromotive force connected to said network forsimultaneously similarly biasing said control electrodes, and means forperiodically changing said electromotive force to periodically changethe biasing of said, control electrodes in succession.

6. A bank of light emitting elements for producing television imageseach within the period of persistence of vision, there being one elementfor each elemental area of the field of view an image of which is to beproduced, a source of image current, a plurality of said light emittingelements being simultaneously directly associated with said source ofimage current, electronic means directly associated with said lightemitting elements for causing them to emit light in succession inaccordance with the variations of said image current, and means forcontrolling said electronic means comprising a delay network, and meansfor causing recurrent impulses tobe propagated along said network.

7. In combination, a plurality of signal producing devices each havingtwo terminals, a source of signaling current connected to a commonterminal of said devices, a plurality of electronic devices each havingan anode-cathode circuit connected to the other terminals 01' saiddevices respectively, each signal producing device being directlyconnected in series with one of said anode-cathode circuits and saidsource of signaling current, and means for controlling said electronicdevices to cause current from said source to energize said signalingdevices in succession.

' 8. In combination, a delay network comprising a plurality of similarsections directly connected in series, each section comprising inductiveand capacitive elements, a plurality of electron disto diflerentsections respectively of said delay netfor controlling said drivingmotor and said elec-.

tronic means for maintaining a desired time relationship between theselection of the rows and the selection of the light producing'elernentsof each row, and means for simultaneously similarly changing thefrequency or phase or the current from said source supplied to saidmotor and said electronic means.

11'. In combination, two electric discharge devices each having acontrol electrode, an anode and a cathode, a source of direct currentconnected in each anode circuit, a source of alternating currentconnected to corresponding portions of said anode circuits, means forconnecting the control electrodes of each device to the anode circuit'of the other device so that current flowing in the anode circuit of oneof said devices will prevent the flow of current in the other of saiddevices, a circuit including a variable condenser and a resistiveelement in shunt with a portion of the anode circuit of one of saiddevices to cause current to flow-alternately in opposite directions insaid condenser circuit, a third electric discharge device the inputcircuit of which is connected to said condenser charging and dischargingcircuit, a source of biasing potenreaching saturation before the currentin said condenser circuit reaches a maximum amplitude.

12. In combination an electric discharge device, an input and an outputcircuit for said device, a source of varying current, means to beenergized by current from said source connected to said output circuit,-commutator means for connecting saidsource-of varying current to saidoutput circuit at intervals, a delay network connected to said inputcircuit, means for impressing an electric impulse upon said delaynetwork to cause said first-mentioned means to 7 pulse upon said delaynetwork.

13. In combination an electric discharge device, an input and an outputcircuit for said device, a series circuit comprising a source ofsignaling current, signal producing means to be energized by currentfrom said source, said output circuit and commutating means forconnecting'said source to said output circuit at intervals, a delaynetwork connected'to said input circuit, means for impressing anelectric impulse upon said delay network at substantially the same timethat said source of signaling current is connected to said outputcircuit to cause said signal producing means to be energized by currentfrom said source of signaling current at a predetermined interval aftersaid electric impulse is impressed upon said delay network.

I I4. In combination a delay network comprising a plurality of sectionsdirectly connected and having a delay characteristic which issubstantially the same for all frequencies over a wide frequency range,means for impressing electric wave energy upon said network, and aplurality of means responsive to said electric'wave energy connected todifferent sections, respectively, of said network.

15. In combination a delay network comprising a plurality of sections,alternate sections of which have different phase characteristics,respectively, such that the phase distortion introduced by one type ofsection is compensated for by the phase distortion introduced by theother type of section to obtain a substantially zero phase. distortioncharacteristic for any pair of connected sections, means .forimpressing'electric wave energy upon said network and a plurality ofmeans responsive to said electric wave energy connected to diiferentsections, respec-- tively, of said network, each of said sectionscomprising an inductive element and a capacitive element, said inductiveelements being directly connected in series.

- 16. In combination a delay network comprising a plurality of sectionsdirectly connected.

5 one section of which has a delay characteristic different from that ofanother section to give an over-all desired delay characteristic, meansfor impressing electric wave energy upon said network, and a pluralityof means responsive to d said electric wave energy connected todifierent sections, respectively, of said network.

17. In combination, an electrical transmission circuit comprising aplurality of delay network sections directly connected in series eachhaving inductive and capacitive elements, means for generating andimpressing upon said transmission circuit an electric impulse having aduration less than 01 second, a plurality of devices responsive to saidelectric impulse electrically is connected to said transmission circuitat positions following different delay sections respectively along thedirection of transmission oi said impulse. I

18. In an apparatus for producing images of so a field of view, anelectrical transmission circuit comprising a plurality ofdelay networksections directly connected each having inductive and capacitiveelements, means for generating and impressing upon said transmissioncircuit an electric impulse having .a duration of the order of theproduct of the reciprocal of the number of elemental areas in the fieldof view and the period of persistence of vision, and a plurality ofdevices responsive to said electric impulse electrically connected tosaid nsmission circuit at positions following diner nt delay sections.respectively along the direction of transmission of said impulse.

18. In apparatus for producing images of a 35 field of view, acombination in accordance with claim 18 in which the delay period ofeach delay section of the transmission circuit is of the order or theduration of said electric impulse.

20. In combination, an electrical transmission circuit comprising aplurality of delay network sections directly connected in serieseach-having inductive. and capacitive elements and a plu- 'rality ofelectric discharge devices having control electrodes connected todifierent delay sections, respectively, means for normally negativelybiasing said control electrodes to reduce the currents flowing in theanode circuits of said electric discharge devices, and means forsimilarly changing the potential of said control electrodes insuccession to permit current of increased amplitude to flow in saidanode circuits, said means comprising means for impressing an electricimpulse upon said transmission circuit.

21. In combination, a bank of light-emitting elements for producingtelevision images, there being one light emitting element-for eachelemental area of the field of view, an image of which is to beproduced, and means for causing Q0 said light emitting elements to beenergized periodically in succession, all within the period ofpersistence of vision, each in accordance with cuits or said electricdischarge devices in succession to cause current from said source oftelevision image current to energize said light producing devices insuccession said last-mentioned means comprising a continuous delaynetwork along which electric impulses may be propagated, means forconnecting said input circuits to diiierent portions 01' said networkrespectlvely along the line of propagation, and means for impressingupon said network impulses the duration of which is less than thepropagation time along said network ifroni one input circuit to thefollowing input circuit along the line of propagation. and the intervalbetween successive impulses being substantially equal to the time ofpropagation from the first input circuit to the last input circuit alongthe line of propagation.

WILLIAM A. KNOOP.

